Carry out the following steps to run the data store query:

1. Navigate to File | Run Datastore Query. Choose the PostGIS connection from the Connection drop-down menu or use the Connection Manager utility if you are not linked to the database.
2. We'll create and name a polygon layer of the main streams in the region by executing the following query:

      SELECT gid, ST_BUFFER("chp11".lines.geom_sp, 75) 
      AS the_geom, fullname 
      FROM "chp11".lines WHERE fullname <> '' AND hydroflg = 'Y'

The preceding query is shown in the following screenshot:

The preceding query selects the lines on the map that represent hydrology units such as "hydroflg" = 'Y' and streams. The selected stream lines (which use the State Plane geometry) are buffered by 75 feet, which should yield a result like that shown in the following screenshot:

3. The ST_Buffer function uses the units of the data projection for buffering. So, if your data still has the original spatial reference EPSG: 4269, you will be buffering the lines by 75 degrees, and this will lead to very strange results indeed! Modify the following SQL query to transform your geometry:

      SELECT AddGeometryColumn('chp11', 'lines','geom_sp',3734,
                               'MULTILINESTRING', 2);
      UPDATE "chp11".lines SET geom_sp = ST_Transform(geom,3734);

4. You'll then want to go back to step 2 in order to create the buffer measured in feet.
5. Next, pan and zoom on the map and find two, separate polygons that are near each other.
6. Select the Fence icon on the main menu, as shown in the following screenshot:

7. Draw a connection (overlapping a connection is fine) between the two unconnected polygons using the Fence tool. Click once on the Fence button to create a vertex and double-click on it once your polygon is complete.
8. Switch over to the Select Features Tool, as shown in the following screenshot, and select the polygons that you drew on either side of the Fence bridge; select multiple features by holding down the Shift key:

You should now have a fence junction between the selected polygons. You should see something similar to the following screenshot:

9. Navigate to File | Run Datastore Query again.
10. This time, we will utilize the buttons to the right-hand side of the window to connect.

Run ST_UNION on the selection and fence together so that the gap is filled. We do this with the following query:

      SELECT ST_UNION(geom1, geom2) AS geom

Use the Selection and Fence buttons in place of geom1 and geom2 so that your query looks as shown in the following screenshot:

11. Click on OK and view the query result by turning off the Main Streams and Fence layers, as shown in the following screenshot: